The present invention relates to a silicone rubber base compound for electrical wire coating, silicone rubber composition for electrical wire coating, and a process for the production of silicone rubber coated electrical wires.
Due to its superior heat resistance, cold resistance, weatherability, electrical characteristics, etc., silicone rubber has found many uses as a material for extrusion molding used for making tubing, tape, sheets, electrical wire coating, and the like. In the past, chlorinated organoperoxides, such as 2,4-dichlorobenzoyl peroxide and chlorobenzoyl peroxide, have been used as the curing agents for curing silicone rubber compositions using in such extrusion molding materials. However, the problem with silicone rubber compositions produced by adding these chlorinated organoperoxides is that they emit offensive odors in the process of curing and cause blooming on the surface of the moldings made of silicone rubber after curing. Blooming is a phenomenon where due to the gradual exudation of curing agent decomposition products on the surface of a molding its surface turns white. Silicone rubber compositions containing added bis(orthomethylbenzoyl) peroxide (Japanese Kokai (Unexamined) Patent Publication No. Sho 59{1984}-18758) and silicone rubber compositions containing added bis(paramethylbenzoyl) peroxide (Japanese Kokai (Unexamined) Patent Publication No. Sho 62{1987}-185750) as the curing agent have been suggested as a means to eliminate such problems. However the problem with these silicone rubber compositions is that their cure rate is slow and voids are liable to be generated in the silicone rubber and when these silicone rubber compositions are used as materials for electrical wire coating they have inferior electrical insulating properties, such as the increased frequency of arcing at high voltages. Although such problems are eliminated to a certain degree if the rate of output of the silicone rubber composition from the extruding machine is lowered and the heat curing time is made longer, the rate of production of silicone rubber coated electrical wires decreases resulting in the disadvantage of increased production cost.
The present inventors have arrived at the present invention as a result of in-depth investigations aimed at eliminating the above described problems. Namely, it is an object of the present invention to provide a silicone rubber base compound for electrical wire coating suitable for use as the main ingredient of a silicone rubber composition for electrical wire coating which is a silicone rubber coating material superior in moldability prior to curing and superior in electrical insulating properties after curing, a silicone rubber composition for electrical wire coating which is a silicone rubber coating material superior in moldability prior to curing and superior in electrical insulating properties after curing, and a process for the production of silicone rubber coated electrical wires.